I've been wondering, what does limit the number of limbs?.For example, nearly all vertebrates are cuadrupedal or have vestigial limbs that add up to 4 limbs, why is it that there are no, let's say, hexapedal ( it would be possible for a, let's say, 4 legs bird? )

Interesting question. I don't have a complete answer, but my guess would be either 1) extra limbs are no great advantage and cost energy or, 2) contingency (that is, things just happened to fall out that way). Gould is famous for having said that if we could "rewind the tape of life" and play it again, we'd get much different results.

Once the basic body plans were established in the Cambrian period, it would have been very difficult for taxa to change their body plan once it was established. Screwing with Hox genes in a complex mammal would probably not result in a viable organism, but screwing with Hox genes in an insect? That can work. My guess would be this is why we see more variation in the number of limbs among arthropods.

If arguing with people on the internet helps me understand science, then I will do it. FOR THE CHILDREN.

Luxorien wrote:Interesting question. I don't have a complete answer, but my guess would be either 1) extra limbs are no great advantage and cost energy or, 2) contingency (that is, things just happened to fall out that way). Gould is famous for having said that if we could "rewind the tape of life" and play it again, we'd get much different results.

Once the basic body plans were established in the Cambrian period, it would have been very difficult for taxa to change their body plan once it was established. Screwing with Hox genes in a complex mammal would probably not result in a viable organism, but screwing with Hox genes in an insect? That can work. My guess would be this is why we see more variation in the number of limbs among arthropods.

That's very interesting!!! Do you have more information about why it wouldn't produce a viable mammal?